The present invention relates generally to integrated circuits (ICs). More particularly, the invention relates to fuses used in ICs.
Fuse cells are widely used in integrated circuits. As an example, fuse cells can be used to store addressing information of defective memory cells in an array for redundancy applications. FIG. 1 shows a conventional fuse cell 101. The fuse cell typically includes a fuse 110 coupled between a pull-up circuit 105 (e.g., Vcc which represents a logic 1) and a pull-down circuit 106 (e.g., ground which represents a logic 0). Depending on the state of the fuse (cut or uncut), the fuse cell generates a fuse cell output signal at a fuse cell output terminal 160 which is commonly coupled to the fuse and pull-up power source. As illustrated, the pull-down circuit is decoupled from the power-up circuit when the fuse is cut, producing a logic 1 fuse cell output signal. On the other hand, an uncut fuse couples the output terminal to the pull-down circuit, thus generating a logic 0 output signal.
In the event the fuse is uncut, a current path exists between the power up and power-down circuits. As a result, power dissipates from the power up circuit to ground when the fuse is uncut. This leads to an increase in power consumption, particularly since one of the design goals is to minimize the need to cut fuses in the IC. For low power or portable applications, particularly, the increased power consumption is undesirable and, in some cases, unacceptable.
As evidenced from the above discussion, it is desirable to provide an improved fuse cell with reduced or no static power dissipation.
The invention relates generally to fuse cells. In particular, the invention relates to software programmable fuses having reduced or no static power consumption. In one embodiment, the fuse cell includes a control circuit, a fuse circuit, a software fuse circuit, and a latch. The control circuit is coupled to the latch, fuse circuit and software fuse circuit. In response to fuse cell input signals, the control circuit causes the fuse cell to operate in either a first or second operating mode. In the first operating mode, the control circuit couples the latch to the fuse circuit, enabling the latch to store the fuse state. In the second operating mode, the control circuit couples the latch to the software fuse circuit. Depending on the fuse state to be simulated, the latch is in a first logic state or a second logic state.
In another embodiment, the control circuit further comprises an initialization circuit. During power up, for example, an active initialization signal is generated. The active initialization signal couples the initialization circuit to the latch to initialize the latch to a first known state. After the latch has been initialized, the fuse cell operates in either the first or second operating mode.